1. Field of the Invention
The present invention relates to a steam turbine-power plant provided with a high-temperature steam turbine, and more particularly to a steam turbine power plant provided with a steam turbine which has individual components comprised of suitable heat-resistant materials.
2. Description of the Related Art
Conventionally, because the individual components configuring thermal power generation facilities are used under steam conditions including generally a steam temperature of 600° C. or less, ferritic heat-resistant steels having outstanding productivity and economical efficiency have been used for main members such as a turbine rotor, a turbine blade and the like which are exposed to high temperatures (see Japanese Patent Publication No. SHO 60-54385, and Japanese Patent Laid-Open Applications No. HEI 2 -149649, No. HEI 6-306550 and No. HEI 8-3697).
In recent years, the thermal power generation facilities are positively made to be more efficient with environmental conservation as a background, and a steam turbine is operated using high-temperature steam having a temperature of about 600° C. Such a turbine has quite a few parts which cannot meet the required properties because of the various properties of the ferritic heat-resistant steels used. Therefore, austenitic heat-resistant steels and the like more excelling in high-temperature properties are used.
But, there were problems that the use of the austenitic heat-resistant steels increased the facility cost, and a thermal stress tended to occur at a time of change in load when the plant was activated or stopped because the austenitic heat-resistant steels had low thermal conductivity as compared with the ferritic heat-resistant steels and also had a high coefficient of linear expansion.
Therefore, it is proposed to configure a steam turbine generating system by restrictively using the austenitic heat-resistant steels for a steam turbine using steam having a temperature of 650° C. or more in comparison with a steam turbine using steam having a temperature of about 600° C. (see Japanese Patent Laid-Open Applications No. HEI 7-247806 and No. 2000-282808, and Japanese Patent No. 3095745). For such a steam turbine generating system, the austenitic heat-resistant steels having outstanding high-temperature properties are mainly used for a high-pressure turbine.
In the above-described steam turbine generating system, the high-pressure turbine is frequently set to have a pressure about four to six times higher than that of an intermediate-pressure turbine, so that the casing configuring the high-pressure turbine, a main steam pipe for guiding steam to the high-pressure turbine, boiler component members and the like are formed thick so to resist a high pressure.
But, the use of the thick austenitic heat-resistant steels increases the facility cost. Besides, the austenitic heat-resistant steels might generate an excessively high thermal stress at a time of change in load when the plant is activated or stopped because it has low thermal conductivity and a high coefficient of linear expansion. Therefore, it is necessary to suppress a load change rate to a low level at the time of activating or stopping the plant, and there are problems that operating characteristics are degraded considerably and the like in comparison with an ordinary steam generating plant.